Hardwood flooring



2 Sheets-Sheet 1 A. ELMENDORF HARDWOOD FLOORING lll Nov. 22, 1966 A. ELMENDORF HARDWOOD FLOORING Filed March 14, 1962 2 Sheets-Sheet 2 United States Patent O 3,287,203 HARDWOOD FLOORING Armin Elmendorf, Palo Alto, Calif., nssignor to Elmendorf Research Incorporated, a corporation of'California Filed Mar. 14, 1962, Ser. No. 179,709 3 Claims. (Cl. 161--123) This invention is in the field of ooring, particularly an improved hardwood flooring which is resistant to denting, and is a continuation-in-part of my copending application Serial No. 100,659, filed April 4, 1961 now abandoned.

A primary purpose of the invention is a hardwood flooring in which the resistance to denting is greater than that of the wood itself.

Another purpose is a hardwood flooring which does not have to be refnished during its lifetime.

Another purpose is a hardwood flooring which provides the traction of vinyl tile ooring.

Other purposes will appear in the ensuing specification, drawings and claims.

The invention is illustrated diagrammatically in the following drawings wherein:

FIGURE 1 is a perspective of a partially laid floor which embodies the principles disclosed herein,

FIGURE 2 is a partial section through one of the flooring squares of FIGURE 1,

FIGURE 2a is a partial section through a modified flooring square, and

FIGURES 3-5 are graphs illustrating the principles upon which this invention is based.

Most of the hardwood flooring installed in homes in the United States today is made of oak, although maple is also used to a substantial extent for gymnasium and commercial floors where eye appeal is of secondary importance. From the point of view of eye appeal, walnut, mahogany, and a number of tropical woods are frequently preferred to oak, but they are all deficient in hardness and are generally not regarded as satisfactory for flooring for that reason. Experience in the manufacture of walnut and mahogany ooring has demonstrated that such iloors dent easily in service and being expensive, marring through denting rapidly depreciates the floor. Denting of soft wood flooring made of vertical grain lumber is also a serious drawback to the extensive use of soft wood such as hemlock, pine and Douglas r for flooring. Gak iloors also dent in service, such dents resulting from nails and heels of shoes, pointed heels of ladies shoes, rolling of furniture and prolonged pressure from furniture casters. While oak floors do not dent as readily as the softer woods, such as walnut and mahogany, the presence of dents is an indication that the door must be renished in time by machine sanding and refinishing. It is for this reason that hardwood oors always call for a minimum thickness in the wearing layer of 1A inch. In the case of hardwood plywood flooring, the top ply must be at least 1/s-inch thick to provide the necessary durability for prolonged service.

Wood floors are available in various types. They may be in -the form of strips with tongue-and-groove or square edges, the latter being nailed to the sub-floor and generally finished on the job. In another form, the wood is used in the form of square blocks, each consisting of several slats, the slats of one block being at right angles to those of the adjacent blocks. The flooring squares may 3,287,203' Patented Nov. 22, 1966 ICC also be in the form of plywood having 1/a-nch veneer faces.

Many different finishing schedules are commonly used on hardwood flooring, such as shellac followed by waxing, shellac plus varnish, or several coats of varnish, or penetrating sealers in combination with wax. In most floor finishes the finish has a thickness ranging from one to three mills (.001-.003 inch). For home use where the oor is subjected to normal wear, the thickness of the varnish coat generally falls within this range. It is customary after several years of use when the finish begins to wear off, to sand the floor and refinish it. Experience has shown that the wood must be at least 1Aa-inch thick to meet this requirement. This minimum thickness is therefore often a requirement in flooring specifications. In the case of penetrating sealer finishes, additional applications of the Sealers are sometimes resorted to as the floor wears, but the major resistance to wear is provided by the wood itself. This is also true of wax finishes.

A main purpose of the present invention is to produce a hardwood oor so made that it does not dent readily, and so nished that the inconspicuous denting of the nish which does take place in time is not objectionable, and so durable that it never wears through during the life of the floor. The wear resistance of the wood itself is never called upon in service. Such finishing becomes possible when the resistance to indentation exceeds that of the natural wood. Printed or wood grain reproductions are not acceptable. The natural wood must be used to get the color and grain variations and the flashV that only natural wood provides.

Many attempts have been made to harden wood by compression and by impregnation, but the effect of such hardening has been either to embrittle the wood, thereby reducing its wear resistance, or to make it so hard that it is slippery when waxed and therefore dangerous to walk on. Excessive hardness is therefore not acceptable.

I have now found that, contrary to accepted theory, under certain conditions, the resistance to indentation of hardwood oors may be increased by reducing the thickness of the wood. I have found that in combining a very thin layer of natural wood with a hard ligno-cellulosic base, if the thickness of the natural wood is reduced, a thickness will be reached at which the resistance to indentation exceeds that of conventional flooring made of this wood, and if thin enough the resistance to indentation may even exceed that of the base to which the wood is bonded. This result is achieved without impregnating the wood or changing its structure, composition or density.

I have found that Douglas r plywood and normal particle boards which are generally used as underlayments for flexible floor coverings are not satisfactory substrates for my purpose. They lack the necessary hardness. The density of underlayments generally ranges from 0.45 to 0.70. I have found that wood fiber hardboards such as tempered Masonite and equivalent products have the necessary hardness and toughness to produce the results desired. The density of satisfactory wood ber hardboard substrates ranges from about 0.85 to 1.15. Other ligno-cellulosic boards, such as certain high density shaving or particle boards are also suitable base materials and adequately hard when their density lies in this range. Cement-asbestos boards of the high density type also have the necessary hardness, dent-resistance, and dimensional stability.

The present invention relates to a wood flooring of the same general thickness as vinyl flooring, namely, /g inch to 1A inch. It is suiciently durable and dent resistant, and is sufficiently pliable so that it can be laid with conventional flooring adhesives using manually applied momentary pressure. This is a requirement of major importance in the field of flooring. In a thickness 4comparable with vinyl t-ile, my flooring is sufficiently flexible so that it follows the contour of the subfloor, but, unlike vinyl tile, it does not telegraph the wood grain of the plywood subflooring or underlayment or joints` in the same. The present flooring requires no edge leveling means such as a tongue-and-groove connection, and it can be laidwith the same procedure and speed as conventional asphalt or vinyl tile. This is a surprising result in view of the unbalanced construction of the flooring. Due perhaps to the thinness of the wood, the slight deviations from flatness that may occur are never serious and do not prevent satisfactory bonding.

When this floor is to be laid over a wood plank subfloor, an underlayment must bev used as with flexible oor coverings such as asphalt tile or vinyl tile. Inasmuch as Douglas tir plywood is one of the commonest underlayment materials, one of the requirements of this improved flooring consists in the necessity for being able to use it successfully on Douglas iir plywood underlayment or subooring. Experience in the application of vinyl tiles to plywood ysubilooring or to plywood underlayment has shown that the nails used in the installation ofthe plywood and the joints between the sections of plywood, as well as surface roughness due to grain raising, will al1 telegraph through the vinyl tile, thereby detracting greatly from the appearance of the oor. This is generally regarded as one of the major liabilities of vinyl tile flooring. I have found that no such telegraphing of joints, nail heads or surface roughness takes place through my improved thin wood ooring of the same thickness as vinyl flooring. The thin hardwood flooring of this invention is suticiently flexible so that it,

follows the contour of the Vsubfloor and successfully bridges joints in the same without telegraphing.`

The oor tile must be suiciently flexible so that the pull or tack exerted by Iconventional ooring adhesives is adequate `to hold the flooring in contact with the subfloor while the adhesive sets. I have found that in order to obtain over-all bonding theV thickness of the high density hardboard base should not be greater than about Ms inch and preferably should be about 1/12 inch. If the base is appreciably thicker than about 1/s inch, some difficulty may be experienced due to the springing away from the subfloor at tile edges while the adhesive is still fresh and edge support as by means of splines becomes necessary. In FIGURE l, the plywood subooring is indicated at and the ooring at 12. The floor tile disclosed consists of a substrate or base 14, preferably of the wood-fiber hardboard or high-density shaving or particle board type described. A natural wood layer 18 is suitably bonded to the base and is of a thickness as described hereinafter. Covering the natural wood layer 18 is a film 16 which is of a clear abrasion-resistant material so that the grain of the natural wood will be visible. The layer 16 will be described hereinafter.

VFIGURE 3 illustrates the results of tests made to determine the optimum thickness of the hardboard base 14. Indentation tests were made using a i-inch steel ball and a pressure of 150 pounds on the ball, on a tempered hard board, having a specific gravity of 1.10, bonded to 3/s-inch Douglas tir plywood. The indentation shown in the graph is the residual indentation two hours after removal of the pressure. A pressure of 150 pounds on the steel ball corresponds to the weight of an average person. The test results indicate that indentation progressively increases with the reduction of thickness of the base until a thickness of about 1&0 inch 4 is reached kat which point the steel ball breaks through. The base must therefore not be thinner than about lo inch. As stated earlier in order to retain the necessary degree of flexibility, the maximum thickness of the base should not exceed about 1A inch, with 1/2 inch being a preferred thickness.

The maximum thickness of the base is determined by the desired flexibility or suppleness of the flooring. The flooring may also be made supple by cutting grooves 20 in the back as shown in FIGURE 2a. These grooves may be V-shaped or rectangular or of any other shape provided their depth is adequate. Grooves are frequenti ly cut in wood llooring where they serve as a means for escape of the adhesive squeezed out in laying the oor. I may use grooves in order to improve the suppleness. For this reason my grooves must be deep enoughto achieve this result. Superior suppleness results when the thickness of the base at the bottom of the grooves,

indicated at 22, is about lyo inch, but some improvement in flexibility -is obtained even when the grooves are shali lower and the thickness at the base is somewhat greater` sure for various thicknesses of veneer. change in the residual indentation after two hours, appears from these tests that the residual indentation was reduced by reducing the veneer thickness if the veneer is bonded to a base that is substantially harder than natural f wood, lsuch as temperer hardboard.

The results shown in FIGURE 4 suggest that a veneer as thin as 1/100 inch could be used if no other factors,lsuch as adhesive strike-through, had to be considered.

It will be noted from FIGURE 4 that when the veneer` is bonded to hardboard as described and the thickness of` the veneer is about .04 inch, the depth of theresidual in-` dentation is .02 inch, about the same as that on a 1s-inch hardboard base alone (FIGURE 3). When the veneer thickness is less than about .04 inch, the depth of indenta-` tion is, surprisingly, even less than that of 1s-inch hard-1 board alone. On the other hand, when the thickness of-` the veneer exceeds about .04 inch, the depth of the residual indentation progressively increases and is greater than the indentation of the 1s-inch hardboard alone. For this reason, it is preferable to limit the veneer thickness to about .04 inch. In this way, the resistance to denting of the hardboard base is utilized to its fullest extent. This same result is pointed up in FIGURES 7 and 8 of copending application Serial No. 100,659, which show the indentation at pounds of pressure when veneers of various thicknesses are bonded to 1z-inch hardboard.

Several synthetic products, such as the polyvinyl chlorides, polyurethanes,and epoxy resins possess the wear resistance required in my flooring ifrapplied in a thickness of at least .005 inch. Under foot ltraflic, finishes made of these products yield suiciently to provide good traction. They are generally softer `than hardwood such as oak.

The finish or surface layer 18 may be applied in the form A 3/16-i11cl1` diameter steel ball was placed on the laminate and sub-` jected to a pressure of 150 pounds. 'Ihe curve shows the` residual indentation two hours after removal of the presi There was no` It f Preferably the thickness ofthe finish 18 is at least ve times as thick as conventional floor finishes, bonded 1 to the Wood. In order to be sufficiently durable, and to ucts yield considerably under pressure so that they dent noticeably if they are thicker than .030 inch. I have found that a coating of clear vinyl resin comparable in physical properties with the clear resin used for vinyl oor tile` may be used with a thickness limitation ranging from about .005 inch to .030 inch.

The entire assembly including the hardboard base, the wood layer and the surface layer are suitably bonded together in a press using pressing conditions in common usage for each bond.

FIGURE 5 shows the results of indentation tests made on several types of commercial flexible floor tile. These tile were all about 1/s-inch thick and were tested for dent resistance. All of the tests were made with a steel ball 3/G-inch in diameter and an applied pressure of 150 pounds. The diagrams illustrate the depth of indentation of each product at a load of 150 pounds, immediately after releasing pressure, one hour after release of pressure, and 24 hours after release of pressure. The tests included hardboard, particle board, oak and maple wood, vinyl tile, both of the solid color type and clear, vinyl asbestos tile, asphalt tile, rubber tile and two tile made from oak and in accordance with this invention. The results shown in the bar diagrams of FIGURE 5 illustrate that commercially-made vinyl tile are relatively soft and dent easily, but on the other hand they recover well. This is particularly true of clear vinyl of the type used for the surface iilm 18. Vinyl asbestos and asphalt tile dent less under load and recover less than vinyl tile. Rubber tile dents easily and does not recover as well as vinyl of the clear type. The diagrams also show that tempered hardboards dent less than vinyl tile. The same applies to high density particle board. Such ooring woods as white oak and hard maple dent more than tempered hardboard, or high density particle board and recover little.

The most surprising results of the tests are illustrated in the bars at the right of FIGURE 5, from which it will be seen that typical floorings of this invention dent less than ooring hardwood such as oak and maple and that the residual dents after 24 hours are no greater than those of clear vinyl tile. Since one of the major advantages of vinyl tile as a flooring `material is its recovery from indentation, the product of this invention is comparable in this property to vinyl tile even though it is much harder and suffers less immediate indentation.

Wear tests were made simulating the abrasion suffered by flooring subjected to heavy foot traic. Observations frequently made have shown that wood oor finishes wear through first at the locations where persons walking on the same change their direction as, for example, at the foot of a stairway or at entrances to doorways. Such tests must be made at pressures corresponding to those of foot traffic and must simulate the abrasionof shoe leather on dusty floors. Such tests were conducted on typical hardwood floors factory-finished by two well-known manufacturers of hardwood fiooring. Similar wear tests were made on products of this invention using a clear vinyl film in a thickness of l2 mils and of a hardness comparable to that ofthe clear vinyl tile illustrated in FIGURE 5. It was found that the thickness of the tinish was reduced less than one mil in the time required for complete destruction of the conventional floor finishes applied by wood ooring manufacturers. On this basis it is to be expected that a vinyl film five mil in thickness will wear at least five times as long as standard hardwood fioor finishes. It may be further concluded that a vinyl film finish thicker than five mil will not wear through for the life expectancy of oors made as disclosed herein. In other words, in actual service the wood in the tile of this invention is never subjected to wear.

The results of tests shown in FIGURES 3, 4 and 5, and FIGURES 7 and 8 of copending application Serial No. 100,659, indicate that the product of this invention is at least as dent resistant as the base material, or tempered hardboard. The base materia-l in turn is harder than common iiooring hardwoods, such as white oak and hard maple. Most -ooring hardwoods are in turn harder tha-n vinyl floorin'gs. 1

The Ilooring tiles of this invention are suitable for bonding to a subfloor yor underlayment with conventional iiooring adhesives using momentary pressure. There are no tongue-and-:groove joints or splines to align the edges and to bring the tile surfaces to the same level. The flooring consists of a lsing-le layer of very thin natural wood 'bonded to a base that is harder than ooring hardwood and that-has a thickness of not less than l/o inch nor greater than 1A; inch. The layer of natural wood, for example oak or walnut is preferably thinner than .04 inch. The thin natural wood is bonded to such a base and is faced with a wear-resistant transparent film comparable in hardness and durability to clear vinyl used for floor tile, and which is so'fter than fiooring hardwood to obtain satisfactory traction.

Although the invention has been generally described as suitable for forming iiooring tiles, it should be realized that flooring planks .may al-so be formed by fdllowing the disclosure herein.

Whereas the preferred Vform of the invention has been shown and described herein, it should 'be realized that there are many modifications, alterations and substitutions thereto within the scope of the following claims.

.I claim:

1. A prefinished wood ooring havin-g a dent resistance exceeding that of ilooring hardwood and which floor-ing is adapted for bon-ding to a subiioor by pressure morn-entari'ly applied and which flooring requires no refinishing after installation, including,

a ligno-cellulosic fibrous base having a-hardness resulting due to a density of from about 0.85 to 1.15, said base having a thickness between about 1/s inch and 1/0 inch to provide Iservioeab'ility under extended use together with adequate flexibility to allow said 'base to follow the undulati-ons in a subfloor when bonded to a suboor with an adhesive while using momentary pressure,

a layer of hardwood veneer, thinner than about 0.04

inch, said veneer bonded to Vsaid base,

and a clear wear resistant covering bonded to the veneer, said covering consisting essentially of a resin iilm havin-g flexibility and softness suficient to provide adequate traction for the installed flooring, and said film having a thickness of at least l0.005 inch.

2. A prenished wood iiooring having a dent resistance exceeding that of tiooring hardwood and which flooring is adapted for bonding to a subfloor by momentarily applied pressure and which hooring requires no refinishing after installation, including,

a ligno-cellu'losic fibrous base having a hardness resulting due -to a density of from about 0.85 to 1.15, said 'base having a thickness -between about 1/s inch and j/20 inch to provide serviceability under extended use together with adequate flexility to allow said 'base to be bonded to a subfloor with an adhesive while using .momentary pressure,

a layer of hardwood veneer, thinner than about 0.04

inch, said lveneer bonded to said base,

a clear wear-resistant covering bonded to the veneer, said covering consisting essentially of a Vinyl resin film having Hexa-bility and softness to provide adequate traction 4for the installed fiooring.

` 3. A prefinished wood iiooring having a dent resistance exceeding that of :flooring hardwood, which iiooring is adapted for bonding to a subiloor by pressure momentarily applied, and which dlooring further -requires no refinishing atter installation, including,

a lgno-cellulosic fibrous base having a hardness comparable to commercial hardb'oard, the bottom of said base having grooves therein to improve the suppleness of the flooring, t-he thickness of the base at the bottom Iof the grooves being about 1/20 inch,

a layer of natural wood veneer, thinner than about 0.04 inch, said veneer bonded to the top of said base,

a clear wear resistant covering bonded to the veneer,

References Cited by the Examiner UNITED STATES PATENTS Smo'lak 161--251 Loetscher 161-268 X Alexander 287-20.92

Franklin 287-2092 Terry 52-510 X Elemendorf 161-114 8 9/1958 Rubenstein 52-229 7/ 1959 Elmendorf 161-123 X` 4/1960 Rayner 161-165 6/ 1961 Zdanowski A117-176 i 10/196'3 Taylor 161-268 Xl FOREIGN PATENTS 1934 France.

10 RICHARD W. COOKE, JR., Primary Examiner.

JACOB L. NACKENOFF, Examiner.

WILLIAM I. MUSHA-KE, I. E. MURTAGH,

Assistant Examiners. 

1. A PREFINISHED WOOD FLOORING HAVING A DENT RESISTANCE EXCEEDING THAT OF FLOORING HARDWOOD AND WHICH FLOORING IS ADAPTED FOR BONDING TO A SUBFLOOR BY PRESSURE MOMENTARILY APPLIED AND WHICH FLOORING REQUIRES NO REFINISHING AFTER INSTALLATION, INCLUDING, A LIGNO-CELLULOSIC FIBROUS BASE HAVING A HARDNESS RESULTING DUE TO A DENSITY OF FROM ABOUT 0.85 TO 1.15, SAID BASE HAVING A THICKNESS BETWEEN ABOUT 1/8 INCH AND 1/20 INCH TO PROVIDE SERVICABILITY TO ALLOW TENDED US TOGETHER WITH ADEQUATE FLEXIBLITY TO ALLOW SAID BASE TO FOLLOW THE UNDULATIONS IN A SUBFLOOR WHEN BONDED TO A SUBJFLOR WITH A ADHESIVE WHILE USING MOMENTATRY PRESSURE, A LAYER OF HARWOD VENEER, THINNER THAN ABOUT 0.04 INCH, SAID VENEER BONDED TO SAID BASE, AND A CLEAR WEAR RESISTANT COVERING BONDED TO THE VEENER, SAID COVERING CONSISTING ESENTIALLY OF A RESIN FILM HAVING FLEXIBILITY AND SOFTENESS SUFFICIENT TO PROVIDE ADEQUATE TRACTION FOR THE INSTALED FLOORING, AND SAID FILM HAVING A THICKNESS OF AT LEAST 0.005 INCH. 